1. Field of the Invention
The present invention relates to an LC filter circuit, a monolithic LC composite component, and a multiplexer used in, for example, a radio communication device such as a portable telephone, and relates to the radio communication device.
2. Description of the Related Art
A conventional monolithic LC filter is shown in FIG. 10. The monolithic LC filter 40 includes an insulating sheet 42 on the surface of which LC-trap coil conductors 50 and 51 are provided, an insulating sheet 43 on the surface of which resonator capacitor conductors 52 and 53 are provided, insulating sheets 44 and 46 on the surfaces of which LC-trap capacitor conductors 54, 55, 58 and 59 are provided, respectively, an insulating sheet 45 on the surface of which input/output conductors 56 and 57 are provided, an insulating sheet 47 on the surface of which a coupling capacitor conductor 60 is provided, an insulating sheet 48 on the surface of which resonator coil conductors 61 and 62 are provided, and insulating sheets 41 and 49 on the surfaces of which ground conductors 63 and 64 are provided, respectively.
The insulating sheets 41 to 49 are laminated, and after insulating sheets for protection are placed on the top and bottom thereof, they are integrally baked. A laminate 67 shown in FIG. 11 is thus produced. The laminate 67 has an input terminal 68, an output terminal 69, relay terminals 70 and 71, and a ground terminal G provided thereon. One end 50a of the LC-trap coil conductor 50 and one end 56a of the input/output conductor 56 are connected to the input terminal 68. A first end 51a of the LC-trap coil conductor 51 and a first end 57a of the output conductor 57 are connected to the output terminal 69. A second end 50b of the LC-trap coil conductor 50, LC-trap capacitor conductors 54 and 58, and a first end 61a of the resonator coil conductor 61 are connected to the relay terminal 70. A second end 51b of the LC-trap coil conductor 51, LC-trap capacitor conductors 55 and 59, and a first end 62a of the resonator coil conductor 62 are connected to the relay terminal 71. Also, the resonator capacitor conductors 52 and 53, the second ends 61b and 62b of the respective resonator coil conductors 61 and 62, and the ground conductors 63 and 64 are connected to the ground terminal G.
FIG. 12 is an electrical equivalent circuit diagram of the monolithic LC filter 40 having the above-described structure. An LC resonator Q1 includes a resonator inductor L1 defined by the resonator coil conductor 61, and a resonator capacitor Cl defined by opposing the resonator capacitor conductor 52 to the LC-trap capacitor conductor 54. Likewise, an LC resonator Q2 includes a resonator inductor L2 defined by the resonator coil conductor 62, and a resonator capacitor C2 defined by opposing the resonator capacitor 53 to the LC-trap capacitor conductor 55. These LC resonators Q1 and Q2 are capacitively coupled through a coupling capacitor C3 defined by opposing the coupling capacitor conductor 60 to the LC-trap capacitor conductors 58 and 59.
An LC trap circuit T1 is inserted between the input terminal 68 and the LC resonator Q1, and an LC trap circuit T2 is inserted between the output terminal 69 and the LC resonator Q2. The LC trap circuit T1 includes an LC trap inductor L3 defined by the LC-trap coil conductor 50, and an LC trap capacitor C4 defined by opposing the LC-trap capacitor conductors 54 and 58 to the input conductor 56. Likewise, the LC trap circuit T2 includes an LC trap inductor L4 defined by the LC-trap coil conductor 51, and an LC trap capacitor C5 defined by opposing the LC-trap capacitor conductors 55 and 59 to the output conductor 57.
In this monolithic LC filter 40, the LC-trap coil conductors 50 and 51 defining the respective LC trap circuits T1 and T2, and the resonator coil conductors 61 and 62 defining the respective LC resonators Q1 and Q2, are provided on separate insulating sheets 42 and 48, respectively. As a result, the area required to provide a conductor pattern defining a coil increases, thereby making it difficult to reduce the size and height of the LC filter 40.
In order to overcome the problems described above, preferred embodiments of the present invention provide an LC filter circuit, a monolithic LC composite component, a multiplexer, and a radio communication device having reduced sizes and heights.
A preferred embodiment of the present invention provides an LC filter circuit including an input terminal and an output terminal, first and second LC resonators electrically connected between the input terminal and the output terminal, an input-side LC trap circuit electrically connected between the input terminal and the first LC resonator, and an output-side LC trap circuit electrically connected between the output terminal and the second LC resonator. A portion of an inductor defining the first LC resonator also provides an inductor defining the input-side LC trap circuit, and a portion of an inductor defining the second LC resonator also provides an inductor defining the output-side LC trap circuit.
Another preferred embodiment of the present invention provides a monolithic LC composite component including a laminate including a plurality of laminated insulating layers, an input terminal and an output terminal provided on the surface of the laminate, first and second LC resonators which are provided in the laminate, and each of which is defined by an LC-resonator inductor conductor and an LC-resonator capacitor conductor, an input-side LC trap including an LC-trap capacitor conductor electrically connected between the input terminal and the first LC resonator, and a portion of the LC-resonator inductor conductor defining the first LC resonator, and an output-side LC trap including an LC-trap capacitor conductor electrically connected between the output terminal and the second LC resonator, and a portion of the LC-resonator inductor conductor defining the second LC resonator.
With these arrangements, since a portion of the inductor L of the LC resonator is arranged to also provide an LC trap inductor L, it is unnecessary to separately provide an LC-trap coil conductor. As a result, an LC composite component having a greatly reduced size and height is achieved.
The multiplexer and the radio communication device according to further preferred embodiments of the present invention include a monolithic LC composite component having the above-described features. This achieves a multiplexer and a radio communication device that are compact and low-profile.
The above and other elements, characteristics, features, and advantages of the present invention will become clear from the following detailed description of preferred embodiments of the present invention in conjunction with the accompanying drawings.